The following relates to the optical arts, optical filter arts, and related arts.
Optical filters with high spectral selectivity can be manufactured using a stack of layers with alternating layers of two (or more) constituent materials having different refractive index values. Such filters are sometimes called interference filters, and can be designed and variously combined to provide a designed pass-band, stop-band, high-pass, or low-pass output. A notch filter can be designed by constructing the stack of layers to form a Bragg reflector blocking a stop-band. The layer stack is deposited on a substrate that is optically transmissive for the wavelength or wavelength range to be transmitted, and may for example be a glass plate for an optical filter in the visible spectrum.
A linear variable filter is similar, but includes a linear gradient in the thickness(es) of one or more layers of the interference filter. The linear gradient produces a corresponding linear gradient in the wavelength (e.g. passband), though the correspondence is not necessarily linear in nature.
Some improvements are disclosed herein.